This disclosure is directed to flame retardant thermoplastic compositions having unexpectedly low smoke density, their methods of manufacture, and methods of use thereof. The compositions are especially useful in the manufacture of components for mass transportation applications, such as rail.
Polycarbonates are useful in a wide variety of applications at least in part because of their good balance of properties, such as moldability, heat resistance and impact properties among others. However, standards for flame retardancy properties such as flame spread, heat release, and smoke generation upon burning have become increasingly stringent, particularly in applications used in mass transportation (aircraft, trains, and ships), as well as building and construction. For example, the European Union has approved the introduction of a new harmonized fire standard for rail applications, namely EN-45545, to replace all currently active different standards in each member state. This norm will impose stringent requirements on smoke density and heat release properties allowed for materials used in these applications. Smoke density (Ds-4) in EN-45545 is the smoke density after 4 minutes determined in accordance with ISO 5659-2, and heat release in EN-45545 is the maximum average rate of heat emission (MAHRE) determined in accordance with ISO 5660-1.
It is exceptionally challenging to develop materials that meet stringent smoke density standards in addition to other material requirements. It is particularly challenging to develop materials that meet these requirements and that have good mechanical properties (especially impact/scratch resistance) and processability. Accordingly there remains a need in the art for thermoplastic compositions that have excellent low smoke properties. It would be a further advantage if the compositions could be rendered low smoke without a significant properties detrimental effect on one or more of material cost, processability, and mechanical properties. It would be a still further advantage if the materials could be readily thermoformed or injection molded.